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High nitrous-oxide emissions from fertilisers clash with climate goals, study finds

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Rising nitrous oxide (N2O) emissions due to the growing use of fertilisers around the world are jeopardising the climate goals of the Paris Agreement, a study has found.

The greenhouse-gas effects of N2O are considered 300 times more potent than carbon dioxide (CO2) and can remain in the atmosphere for more than 100 years.

Researchers from Auburn University in the US and the University of East Anglia in the UK aimed to produce the most comprehensive assessment to date of all global sources and sinks of N2O.

Their findings show N2O emissions are increasing faster than any emission scenario developed by the Intergovernmental Panel on Climate Change (IPCC), consistent with greenhouse gas scenarios that lead to global mean temperature increases well above 3°C from pre-industrial levels.

The Paris Agreement aims to limit warming to less than 2°C but ideally no more than 1.5°C.

The study points to an alarming trend affecting climate change: N2O has risen 20 per cent from pre-industrial levels – from 270 parts per billion (ppb) in 1750 to 331ppb in 2018 – with the fastest growth observed in the last 50 years due to emissions from human activities.

Study co-leader Professor Hanqin Tian from Auburn University said: “The dominant driver of the increase in atmospheric nitrous oxide comes from agriculture, and the growing demand for food and feed for animals will further increase global nitrous-oxide emissions.

“There is a conflict between the way we are feeding people and stabilising the climate.”

Like CO2, N2O is a long-lived greenhouse gas and is also currently the most significant human-induced agent depleting the stratospheric ozone layer, which protects Earth from most of the Sun’s harmful ultraviolet radiation

The study presents a comprehensive global N2O inventory that incorporates both natural and human-related sources, and accounts for the interaction between nitrogen additions to the earth system and the biochemical processes that control N2O emissions.

It covers 21 natural and human-related sectors between 1980 and 2016.

Human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30 per cent over the past four decades to 7.3 teragrams of nitrogen per year.

The analysis also reveals an emerging N2O-climate ‘feedback’ resulting from interactions between nitrogen additions to crops for food production and global warming, further enhancing emissions derived from agriculture.

The largest regional contributors to global N2O emissions are East Asia, South Asia, Africa and South America, with Brazil, China and India seeing highest growth, the study said.

Emissions from synthetic fertilisers dominate in China, India and the USA, while emissions from using livestock manure as fertiliser make up the majority in Africa and South America, the study found.

Study co-leader Dr Josep Canadell said: “This new analysis calls for a full-scale rethink in the ways we use and abuse nitrogen fertilisers globally and urges us to adopt more sustainable practices in the way we produce food, including the reduction of food waste.

“These findings underscore the urgency and opportunities to mitigate nitrous-oxide emissions worldwide to avoid the worst of climate impacts.”

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